1. Field of the Invention
Embodiments of the invention generally relate to a substrate support for supporting a substrate in a semiconductor processing chamber.
2. Description of the Related Art
Many semiconductor processes are typically performed in a vacuum environment. For example, physical vapor deposition (PVD) is generally performed in a sealed chamber having a pedestal for supporting the substrate disposed therein. The pedestal typically includes a ceramic substrate support that has electrodes disposed therein to electrostatically hold the substrate against the ceramic substrate support. A target generally comprised of a material to be deposited on the substrate is supported above the substrate, typically fastened to a top of the chamber. A plasma is formed from a gas such as argon that is supplied between the substrate and the target. The target is biased causing ions within the plasma to be accelerated toward the target. The ions impacting the target cause material to become dislodged from the target. The dislodged target material is attracted towards the substrate and deposits a film of material thereon.
Temperature control of the substrate during deposition is one consideration for good deposition performance. Generally, the temperature of the substrate is regulated by transferring heat between the substrate and the substrate support. As heat transfer in the vacuum environment of the process chamber is inefficient, a backside gas, such as argon or helium, is disposed between the substrate and the ceramic substrate support as a heat transfer medium.
Many substrate supports incorporate features which space the substrate from the support surface thereby providing a plenum for backside gas. Generally, these features maintain the substrate in a spaced-apart relation to the support surface at a distance that maximizes heat transfer through the backside gas. Although the optimal distance varies with the specific gas or gases used, the distance between the support surface and the substrate across the plenum is generally maintained at less than about 40 xcexcm in conventional designs.
Generally, backside gas is provided to the plenum through a central conduit disposed near the center of the substrate support. As the space between the substrate and substrate support is narrow, the pressure drop of the backside gas flowing radially outward across the support surface often prevents uniform distribution of a backside gas across the full radial width of the plenum. The non-uniformed distribution of backside gas generally creates a concentration of backside gas near the center of the support, thus causing a higher rate of heat transfer in the center area as compared to the heat transfer rate near the substrate""s edge. This results in temperature gradients on the substrate and correspondingly, poor process performance.
Therefore, there is a need for a substrate support having improved heat transfer characteristics.
A substrate support for supporting a substrate in a semiconductor process chamber is provided. In one embodiment, the substrate support generally includes a first side that supports the substrate and a second side disposed opposite the first side. The first and second sides are coupled by a perimeter. A ring and a plurality of substrate support pads extend from the first side. The ring is disposed proximate the perimeter of the substrate support. A fluid passage is disposed through the substrate support and is coupled to a well disposed in the first side. A plurality of gas flow channels are disposed in the first side and orientated radially outward from the well to a perimeter channel disposed radially inward and adjacent to the ring. The well and channels are adapted to provide uniform distribution of backside gas across the first side of the substrate support.